In the conventional public switched telephone network (PSTN), there is a close association between elements that carry voice traffic and elements that manage telephony services, such as call setup and teardown. This close association is not just a result of technical advantages, but also a result of telecommunications policy, which for many years allowed telephone services to be run as a regulated monopoly. One desirable outcome of this close association is that call management elements can easily monitor and directly control the state of the switches and links that carry voice traffic.
In the future, telephony services will be provided in a more open and dynamic fashion. In the emerging network model, control of voice services and transport of voice data are independent functions that may be provided by two or more independent service providers. The independence of voice service and data transport raises the question of how to allow a service provider, which offers call services, to directly control the network of the business that offers the data transport. The owner of the network that transports voice will likely be unwilling to give direct control to the call service provider, and may even be unwilling to reveal to the call service provider the details of the network topology, capacity, and current status, among many other factors bearing on the availability and quality of communication services.
The above situation is further complicated for end-to-end voice transmission as well as real-time transfer of audio and video, because multiple networks may be traversed to deliver the data. Each of these networks may be independently operated. Further, multiple service providers, such as long distance providers and cable companies, may be involved as well. As such, there is a need for an effective way for a service provider to authorize the use of resources in data transport networks without knowing who will process the authorization.
A couple of solutions have been proposed; unfortunately, each proposal is less than desirable. The first proposal was provided by the Packet Cable Consortium and related telephone services over cable networks. The Packet Cable Consortium proposed a model in which a telephony call server directly communicates its authorization of resource reservation to each of the devices that implement that reservation. The assumption behind these standards is that there is only one provider, which provides both the voice transport and the call services. As discussed above, such a technique will likely be ineffective in the emerging network model containing independent service and network providers.
In a document recently presented to the Internet Task Force (ITF) standards body, the Packet Cable Consortium proposed a different model acknowledging the possibility of multiple network and service providers. However, if the model still operated under the assumption that the call service elements know how to directly communicate with and control the elements in the transport networks that are responsible for resource reservation. Again, this limiting assumption does not fit the open environment of the emerging communication network model. Thus, there remains a need for an effective way to authorize the use of resources without requiring the network provider to directly communicate with the service provider to reserve resources throughout the network to initiate authorization.